The letter was reportedly typed on Clarence House notepaper and signed by the Prince in Arabic.

A letter from Mr Blair was also found in which he praised Gaddafi for having "led a genuine transformation in relations between our two countries".

A spokesman for Mr Blair said: “Gaddafi was received in several European capitals, including Brussels, Rome and Paris.

“There was, therefore, at that time no reason whatsoever for not continuing to engage with him, especially since Mr Blair in office had been responsible for getting Gaddafi to give up his chemical and nuclear weapons programme and renounce terrorism.”